The present invention relates to a semiconductor light-emitting device utilized in an LED (Light Emitting Diode) in use for a light source for a backlight of a liquid crystal display, cellular phone, mobile data terminal or the like, a display device utilized in indoor or outdoor advertisements or the like, an indicator of various portable equipment, a backlighted switch, a light source for OA (Office Automation) equipment or the like. The present invention relates, in particular, to a semiconductor light-emitting device in which the wavelength of outgoing light from a semiconductor light-emitting element is converted by using a fluorescent substance and which can be utilized as a light source of various luminous colors and a light-emitting display device using the same.
A semiconductor light-emitting device, characterized by its small size and low power consumption, can emit high-brightness light in a stable manner and thereby is widely used as a light source in various display devices. Furthermore, the semiconductor light-emitting device is also utilized as a light source for reading data records in various data processors. A semiconductor light-emitting element in use for a semiconductor light-emitting device that emits long-wavelength visible light, which has been widely used in practice, can emit high-brightness light from red to green depending on the semiconductor material, formation conditions or the like of a light-emitting layer to be used. Meanwhile, a semiconductor light-emitting element that emits short-wavelength visible light from blue to purple has been developed in recent years and started being used in general practice.
A LED display utilizing a semiconductor light-emitting device having luminous colors of, for example, three primary colors, R (Red), G (Green) and B (Blue), by using semiconductor light-emitting elements of these various luminous colors has started to be commercially available.
Furthermore, Patent Publication No. 2927279, for example, discloses a semiconductor light-emitting device wherein a semiconductor light-emitting element emitting short-wavelength visible light from blue to purple and a fluorescent substance are combined to obtain white by mixing colors of outgoing light from the semiconductor light-emitting element and light whose wavelength is converted by the fluorescent substance.
Japanese Patent Laid-Open Publication No. 10-163535 discloses a semiconductor light-emitting device wherein a semiconductor light-emitting element having blue or blue purple luminous color and one or more kinds of fluorescent substances that absorb light from this semiconductor light-emitting element to emit light in the visible range are combined to obtain high-brightness compact white luminous colors. The luminous colors of the semiconductor light-emitting element and the luminous colors of the fluorescent substances are in mutually complementary color relations. The fluorescent substance is selected so that the luminous color of the semiconductor light-emitting element and the luminous color of the fluorescent substance are added to emit white light.
Furthermore, Japanese Patent Laid-Open Publication No. 10-12925 discloses a semiconductor light-emitting device having a semiconductor light-emitting element that emits ultraviolet light and near-ultraviolet light and a fluorescent substance that emits fluorescent light by light from this semiconductor light-emitting element. This semiconductor light-emitting element is usually a semiconductor light-emitting element that emits blue light, but emits ultraviolet light and near-ultraviolet light by allowing a pulsed high current to flow. It is disclosed that a plurality of luminous colors can be obtained by using a single kind of semiconductor light-emitting element only by changing the kind of fluorescent substance.
Furthermore, Japanese Patent Laid-Open Publication No. 9-153644 discloses a dot-matrix type display device having a light-emitting layer that is formed by using a group-III nitride substance semiconductor and emits ultraviolet rays having a peak wavelength of 380 nm and three kinds of fluorescent substance layers, which receive the ultraviolet rays from this light-emitting layer and emit light in three primary colors, red, blue and green, respectively.
However, these conventional techniques have problems as described below.
A semiconductor light-emitting element having luminous colors from red to green for use in a long-wavelength visible light semiconductor light-emitting device and a semiconductor light-emitting element that emits short-wavelength visible light from blue to purple vary in materials to be used and element shapes depending on the wavelengths of their emitted light. Therefore, when semiconductor elements having different wavelengths are mounted to obtain a semiconductor light-emitting device, a plurality of different mounting materials and different mounting processes are required and the manufacturing process becomes complicated with increased costs.
Furthermore, currents to the plurality of semiconductor light-emitting elements need to be adjusted to obtain white light in a favorable color by using a plurality of semiconductor light-emitting elements having different luminous colors. Therefore, a problem arises that the semiconductor light-emitting device becomes complicated. Furthermore, when a light-emitting display device is formed by using a plurality of the semiconductor light-emitting devices, a large amount of color tones of the semiconductor light-emitting elements need to be adjusted and thus the manufacturing process becomes complicated.
Furthermore, in the semiconductor light-emitting devices disclosed in the above Patent Publication No. 2927279 and Japanese Patent Laid-Open Publication No. 10-163535, the colors of the outgoing light from the semiconductor light-emitting element and the light emitted from the fluorescent substance, which is in complementary color relations with this outgoing light, are mixed to obtain white luminous color. This results in poor light use efficiency is and an unfavorable color tone. For example, when a semiconductor light-emitting device wherein white light is obtained by mixing blue outgoing light of the semiconductor light-emitting element and yellow outgoing light of the fluorescent substance is used as a backlight of a liquid crystal display device, this white light contains a small light quantity of pure green and pure red. Therefore, there is a small quantity of light that transmits a red color filter included in the liquid crystal display device. When the liquid crystal display device performs a full color display, an impression of decoloration is generated.
Furthermore, since a pulsed high current is applied to the semiconductor light-emitting element in the semiconductor light-emitting device disclosed in Japanese Patent Laid-Open Publication No. 10-12925, the semiconductor light-emitting element is destroyed or heated and deteriorated, resulting in a short life and low reliability. Furthermore, since this semiconductor light-emitting element has its emission wavelength peak in the ultraviolet or near ultraviolet wavelength range as well as in the blue wavelength range, this blue light is mixed with the light emitted from the fluorescent substance, resulting in a poor color tone. Furthermore, when the semiconductor light-emitting device is deteriorated, a plurality of semiconductor light-emitting elements having different luminous colors are not uniformly deteriorated in brightness, but a blue-wavelength component is particularly rapidly deteriorated, resulting in changed color tones of the semiconductor light-emitting device. Furthermore, since the semiconductor light-emitting element emits light having wavelengths from the vicinity of near ultraviolet (390 nm) to the ultraviolet range on the short wavelength side, a measure for preventing influences on human bodies needs to be taken. Furthermore, since a resin for fixing and molding the semiconductor light-emitting element is also adversely affected by the light having wavelengths in the ultraviolet range, lower reliability due to deterioration of the fixing resin or lower brightness of emitted light due to blackening of the molding resin may occur.
Since the semiconductor light-emitting device disclosed in Japanese Patent Laid-Open Publication No. 9-153644 also utilizes light having an emission wavelength of 380 nm in the ultraviolet range, a measure for preventing leakage of light in the ultraviolet range needs to be taken to prevent influences to human bodies. Furthermore, a resin for fixing and molding a semiconductor light-emitting element is adversely affected, thereby resulting in deterioration of reliability and lower brightness of emitted light. Since the fluorescent substance layers for emitting three primary colors of red, blue and green are formed on a substrate as well as a semiconductor layer in this semiconductor light-emitting device, the process for manufacturing the semiconductor light-emitting device is complicated, thereby deteriorating the yield and reliability.